This invention relates generally to liquid filtration systems and, more specifically, to traveling bridge-type cleaning apparatus for sequentially cleaning a plurality of suspended solids filter units, some of which are upflow filters and some of which are downflow filters.
It is well known in the art to utilize filtration tanks divided into a plurality of identical filter cells, one adjacent the other, and all containing a multi-layer arrangement of granular filter media such as sand, gravel and the like. In downward flow filtration systems of this type, water or other liquid containing suspended solid particles is introduced into the filtration tank from above and filtered water is drawn off from a chamber beneath the filter cells. During downward flow through the individual cells, particulate matter is entrapped within the layers of granular filter media. Eventually, the particulate matter clogs the filter media, thereby reducing the filtering capability of the system. Thus, there is a need for periodic cleaning of the filter cells. It is also known to maintain such units in continuous operation during cleaning by the use of traveling bridge devices which move from one filter cell to the next, to clean individual cells while permitting the filtration process to continue in the remaining cells.
Examples of traveling bridge apparatus of this type may be seen in U.S. Pat. Nos. 4,540,487; 4,486,307; 4,133,766; 3,984,326, 2,235,227, and 649, 409. Typically, traveling bridge systems include an overhead carriage, movable along tracks, guideways or the like, which carries, e.g., a backwash hood successively engageable with the upper end of each filter cell. For a downflow type filter, water or other treatment liquid is generally introduced into the cell from below, in a counterflow arrangement to the normal filtering direction. The backwash hood typically includes a suction head for drawing out fluid and debris forced to the surface of the filter cell as a result of the backwash. As the backwash of individual cells is completed, the carriage will index the backwash hood to the next adjacent cell. See, for example, U.S. Pat. No. 4,308,141, in which a modular filter system is disclosed, and wherein a traveling bridge type backwash system is indexed to successive filter units.
Other travelling bridge constructions for use in liquid filtration systems are disclosed in commonly owned U.S. Pat. No. 4,859,330 and Ser. No. 07/301,715 filed Jan. 26, 1989 and now allowed.
In the present invention, a unique combination of filter cell cleaning devices is provided in a traveling bridge configuration. Specifically, a single hood assembly is provided which includes both air scour means and backwash means for individual or combined simultaneous use, depending on the type of filter cells to be cleaned.
More specifically, the present invention is designed primarily for use with a tank containing a plurality of roughing filters followed by a plurality of polishing filters. Roughing filters are typically upflow filters designed to entrap larger or coarser particles, while polishing filters are typically downflow filters designed to entrap smaller or finer particles. The present invention, for the first time, permits both types of filters to be effectively cleaned by a single unit in a traveling bridge system.
In one exemplary embodiment, an elongated, rectangular filtration tank is divided into a roughing filter portion and a polishing filter portion. In both portions, the filter cells are defined by a plurality of laterally spaced, substantially parallel partitions extending across the entire width of the tank. The principal distinction between the roughing and polishing filter cells relate to depth of the cell and size of the media contained therein. Thus, the roughing cells are deeper, i.e., the cell bottom wall is located closer to the tank bottom wall, and the filter media comprises a single layer of gravel or anthracite in the 4 mm range. In the polishing filter portion of the tank, the depth of the polishing cells is less, i.e., the cell bottom wall is located farther away from the tank bottom wall, thereby creating a larger chamber between the cell and tank bottom wall. In addition, polishing filter media may include a multi-layer bed ranging from fine to coarse particles.
The tank is further provided with tracks or guideways supporting a traveling bridge for movement along the top of the tank, in a direction transverse to the orientation of the upright partitions. The traveling bridge includes a carriage which carries air scour means and backwash means within a single hood structure adapted for successive engagement with each filter cell. In this regard, the side walls of the hood are laterally spaced apart a distance corresponding to the space between the cell partitions walls, so that the hood may sealingly engage each of the cells in succession. In this regard, the hood is provided with sealing means, such as rubber gaskets, at the lower end of each of the vertical side walls thereof, which engage the upper surfaces of the cell partition walls, thereby isolating the cell from the remaining cells.
An air scour supply conduit extends between the interior of the hood and the carriage. The air scour supply conduit is connected at its upper end to a blower or other source of pressurized air mounted on the carriage. The lower end of the air scour supply conduit, located within the hood, is provided with a flanged head or boot adapted to successively engage vertical risers extending upwardly from the lower end of each roughing filter cell to the upper end thereof, approximately mid-way along the length of the cell. In this first exemplary embodiment, a horizontal air supply conduit is connected to the lower end of each vertical riser and extends across the lower half of each filter cell, preferably within the lower portion of the single layer of filter media, and in a direction substantially parallel to the cell partitions. Each such horizontal conduit is provided with a plurality of perforations along its length and about its periphery so that, when air is supplied to the filter cell via the air scour supply conduit, it will be uniformly discharged along the lower end of the cell, within the layer of filter media. As the air flows upwardly through the filter media, it dislodges particulate matter which will be removed during a simultaneous backwash. The air utilized in the air scour step is eventually vented to atmosphere, preferably by conduit means extending from the interior of the hood upwardly to a point above the level of water in the tank.
Also mounted within the single hood structure is a conventional backwashing device including a horizontal backwash suction conduit. The horizontal backwash suction conduit is located within an upper portion of the hood, above the air scour inlet, and is connected substantially midway along its length to a vertical suction conduit extending upwardly, through the hood, to the carriage. The carriage also mounts a suction pump, the outlet side being connected to the vertical suction conduit. Like the horizontal air supply conduits within the cells, the horizontal backwash conduit in the hood has a length substantially equal to the length of the individual cells. The suction conduit is also provided with a plurality of uniformly arranged apertures extending along its length and about its periphery to uniformly draw liquid and accompanying debris out of the filter cell, for example, in the opposite direction of normal filter flow in the polishing filters.
The hood is also provided with a plurality of inclined baffles extending substantially the length of the hood, and arranged to separate air and liquid within the hood so that the backwash suction conduit does not draw air from the air scour operation into the suction pump.
In use, the air scour and backwash means are operated simultaneously for cleaning the polishing filter cells, While only the air scour means are used to clean the roughing filter cells.
The combination of a simultaneous air scour/backwash operation, carried out successively for each polishing filter cell, and air scour operation for each polishing filter cell, quickly and effectively cleans all of the filter cells and filter cell media in the tank without disturbing the overall operation of the filtration system.
It will be appreciated that in order to index the hood assembly to successive cells along the filtration tank, the assembly is reciprocable vertically by a distance sufficient to enable the hood structure to disengage from the cell partitions or walls, and to clear the adjacent cell partitions during lateral movement to the next cell. To this end, a portion of each of the vertical air scour conduit and vertical backwash conduit, respectively, may be provided with a flexible, e.g., bellows-type, connector which permits a relatively small degree of vertical movement of the hood structure relative to the vertically fixed carriage.
In a related aspect of the invention, the vertical air scour riser provided in each roughing filter cell may be fitted with a spring loaded valve at its upper end, the valve opening in response to air pressure supplied through the air scour supply conduit when the riser and supply conduit are in engagement.
It is also a feature of this invention that the air scour supply conduit boot mount a squeeqee-type device to remove debris from the upper surface of the valve. In an alternative mode, the squeegee-type device may be eliminated and the air scour pump can be actuated just prior to engagement of the air supply conduit and the riser valve to supply a burst of air which will clean the valve head.
Accordingly, in its broadest aspect, the present invention relates to a traveling bridge filter cleaning system including a liquid filtration tank divided into a plurality of adjacent filter cells, a first group of which are roughing filters and a second group of which are polishing filters, each group of cells containing filter media appropriate for its purpose. A traveling bridge carriage is located above the tank and movable along the tank, the carriage mounting air scour means and backwash means within a single hood adapted to sealingly engage successive ones of the roughing and polishing cells.
It will therefore be appreciated that the present invention provides a unique combination of air scour and backwash means in a traveling bridge filter cleaning system which effectively cleans successive cells of a multi-function tank without disturbing the filtering process in the remaining cells.
Additional objects and advantages of the subject invention will become apparent from the detailed description which follows.